According to the Center for Responsive Politics, "spending by organizations that do not disclose their donors has increased from less than $5.2 million in 2006 to well over $300 million in the 2012 presidential cycle and more than $174 million in the 2014 midterms." The New York Times editorial board has opined that the 2014 midterm elections were influenced by "the greatest wave of secret, special-interest money ever raised in a congressional election."
The term was first used by the Sunlight Foundation to describe undisclosed funds that were used during the United States 2010 mid-term election. Its practical effect has been described by Donald Trump as Congress "being under the magical spell of the donors."
In some elections, dark money groups have surpassed traditional political action committees (PAC) and "super PACs" (independent-expenditure-only committees) in the volume of spending. In 2014, the group Freedom Partners was identified as the "poster child" for the rise of dark money. In 2012, Freedom Partners had the ninth-highest revenues among all U.S. trade associations which filed tax returns that year, more than "established heavyweights" such as the American Petroleum Institute, PhRMA, and U.S. Chamber of Commerce. Freedom Partners largely acted as a conduit for campaign spending; of the $238 million it spent in 2012, 99 percent went to other groups, and Freedom Partners itself did not have any employees. This was a major distinction between other high-revenue trade associations, which typically have many employees and devote only about 6 percent of spending to grants to outside groups.
The largest and most complex network of dark money groups are funded by conservative billionaire business magnates Charles and David Koch; the Koch brothers' network accounted for about a quarter of dark money spending in 2012.
The rise of dark money groups was aided by the U.S. Supreme Court decisions in FEC v. Wisconsin Right to Life, Inc. (2008) and Citizens United v. FEC (2010). In Citizens United, the Court ruled (by a 5–4 vote) that corporations and unions could spend unlimited amounts of money to advocate for or against political candidates.
According to the Center for Responsive Politics, dark money (which it defined as funds from outside groups that did not publicly disclose donors, plus groups that received a substantial portion of their contributions from such nondisclosing groups) accounted for nearly 44% of outside spending in the 2010 election cycle.
In the 2012 election cycle, more than $308 million in dark money was spent, according to the Center for Responsive Politics. An estimated 86 percent was spent by conservative groups, 11 percent by liberal groups and 3 percent by other groups.